Divine Incorporeality and the Causal Interaction Problem

Dr. Craig gives a technical lecture on Divine Incorporeality for a conference on philosophical theology entitled “Theism: East and West” at the Sharif University of Technology in Tehran, Iran.

Hello. This is William Lane Craig. Today I’d like to share some thoughts with you about divine incorporeality and the causal interaction problem.

Fundamental to Christian theology is the conviction that God is an incorporeal being. Despite the etymology of the word, by divine incorporeality we do not mean that God is without a body—indeed, according to the Christian doctrine of the incarnation, God the Son does have a human body since the moment of his assumption of a complete human nature in Mary’s virginal conception of Jesus—but rather that God is an immaterial being. Just as the human soul, whether embodied or disembodied, is taken by anthropological dualists to be an immaterial being, so God, whether bodiless or incarnate, is an immaterial substance distinct from the world.

The Coherence of Divine Incorporeality

What objections, then, might be raised against divine incorporeality? This question intersects significantly with discussions in the philosophy of mind. On the contemporary scene, anthropological dualism is a well-represented minority position in the philosophy of mind.^[1] In a theological context anthropological dualism takes the form of body/soul dualism, according to which a human being is a composite of a rational soul and body. On theism God is a sort of soul or mental substance distinct from the physical world.

Physicalism of any variety is obviously incompatible with divine incorporeality, since God is an immaterial mental substance Who is causally connected to the world. Accordingly, if there were good arguments for physicalism, we should have good reason to reject divine incorporeality. But here caution is in order, for divine incorporeality does not obviously entail anthropological dualism. There are on the contemporary scene plenty of anthropological monists, or physicalists, who are Christian theists who affirm divine incorporeality.^[2] Thus, arguments against anthropological dualism do not obviously commit one to a denial of divine incorporeality.

This distinction is highly significant because the most important and widely accepted arguments against anthropological dualism are scientific in nature, what Dean Zimmerman aptly calls “Ockhamist objections” to dualism, to wit, the soul or mind is not needed to account for the empirical data of the cognitive sciences, rendering the hypothesis of the soul dispensable.^[3] Now whatever one thinks of such Ockhamist objections to anthropological dualism,^[4] they are obviously inapplicable to theism because God is not related to the world as soul is to body, much less have we any scientific data about the workings of God’s mind in relation to the cosmos!

What we need to consider, then, are arguments for physicalism that are not scientific in nature but would have application to God as an immaterial mental substance distinct from and causally active in the world. This is a welcome relief, for it prevents our being sucked into the black hole of the literature on the mind/body problem. We can set aside for now as irrelevant Ockhamist objections to anthropological dualism and even forego the positive arguments of substance dualists for anthropological dualism. Of course, if those arguments are sound, so much the better for theism! But we have good scriptural reasons for thinking God to be incorporeal. That is where we as Christian theologians begin. Our question is thus sharply delimited: what arguments are there that God cannot be incorporeal? There are such arguments, but they are much fewer in number than the arguments against anthropological dualism.

The Causal Interaction Problem

Doubtless the most important non-scientific objection to substance dualism is that it posits a causal connection between mind and matter that is utterly mysterious.^[5] We have no understanding how a non-physical substance could have physical causal effects. The objection thus presents a challenge to dualism-interactionism, the view that the mind and body are causally interactive.

Moreland and Rickabaugh distinguish two issues with regard to the interaction problem. On the one hand, it may be a demand for some sort of mechanism between mental and physical entities in virtue of which they interact with one another. This demand is, however, inept, since the effect of the mind upon the body, on pain of embarking on an infinite regress, is taken by dualist-interactionists to be immediate, without any intervening causal linkage.

On the other hand, if the question is taken as simply an expression of scepticism that there could be such immediate causal connections, then the force of the objection can be easily exaggerated. Taliaferro finds the physicalist critic somewhat hard-pressed to provide evidence that the only causal relations possible are among physical objects.^[6] After all, souls, in contrast to causally effete abstract objects like numbers, are concrete entities endowed with causal mental powers sufficient for effects like thoughts. Why not powers to affect the physical realm as well? The materialist cannot simply charge that evidence is completely lacking for mental/physical interaction, Taliaferro reminds us, for if we follow the precept of trusting appearances until we have strong reason otherwise, it seems that the mental and physical do interact.^[7]

Keith Yandell explores and rejects various justifications of such scepticism, for example, that mind/body interaction would violate some supposedly necessary truth like: Only like can affect like, or Only what is in space can affect what is in space, or Ultimate connections cannot be brute. The above causal likeness principle is patently false, so that “anyone should be ashamed for basing criticisms of anything on it.”^[8] As for the spatiality principle, there is just no evident incoherence is stating that something which is non-spatial affects something that is spatial. Considerations from contemporary cosmology reinforce Yandell’s point. There is no reason why something to which our 4D spacetime manifold is present but which exists at no spacetime point in it cannot causally affect things which do exist at various spacetime points. In fact, this is precisely what the initial cosmological singularity does. Granted, it, too, is a physical reality, if real at all, but it is not at all obvious that a God who transcends space and time could not act to produce effects in it. As for the no brute connections principle, Yandell points out that there can be irreducible physical laws connecting physical phenomena, and there is no reason why brute mental-physical connections should be objectionable, whereas brute physical-physical connections are not objectionable.

We may not agree with William Hasker that the problem of causal interaction “may well hold the all-time record for overrated objections to major philosophical positions,” but its force should not be exaggerated.^[9] Hasker is not alone in pointing out that one reason it is not decisive is that “all causal relationships involving physical bodies are at bottom conceptually opaque. We have no ultimate insight into the causal relations involved except to say, ‘That’s the way things are.’”^[10]

In Defense of Causal Interaction

Perhaps the most powerful response to the causal interaction objection by anthropological dualists is that we have good positive reasons to think that the soul is an immaterial substance that causally affects the body, even if we do not understand how.^[11] Moreland and Rickabaugh point out that dualist entities like conscious states and the soul are not only entities of which we have direct acquaintance, but entities whose reality is supported by philosophical arguments from the unity of consciousness, the possibility of disembodied survival or body switches, the best view of an agent in support of libertarian agent causation, the metaphysical implications of the use of the indexical “I,” and the special sort of diachronic and synchronic unity of human persons.^[12]

Similarly, in considering physicalist objections to divine incorporeality, we must not forget that we have sound theistic arguments that support divine incorporeality. Arguments such as the kalām cosmological argument, the teleological argument from the fine-tuning of the universe, and the argument from the uncanny applicability of mathematics in physics provide powerful reasons for thinking that there is a transcendent Mind who has created the universe. These arguments provide a strong cumulative case in support of divine incorporeality that may well outweigh the putative defeaters brought against the doctrine. In particular, they outweigh expressions of incredulity based on our ignorance of how the mental affects the physical.

The Causal Closure of the Physical and
the Evolutionary Argument Against Naturalism

In fact, it seems to me that the dualist-interactionist can turn the tables and argue cogently that the materialist claim that causal interaction is impossible is incapable of rational affirmation. I have reference here to Alvin Plantinga’s celebrated Evolutionary Argument against Naturalism (EAAN).^[13] Plantinga argues that naturalism is self-defeating because if our cognitive faculties have evolved by naturalistic processes, they are aimed, not at truth, but at survival, and so cannot be relied on to produce true beliefs. Because our mental states (assuming against the eliminative materialist that we have such states) have absolutely no effect on our brain states, the content of our beliefs is irrelevant to our survivability. All that matters is our physical behavior, not the truth of our beliefs. So long as we act in ways conducive to survival, it literally does not matter what we believe. But if we cannot rely on our cognitive faculties to produce true beliefs, then the belief in naturalism is itself undermined, since it has been produced by those very cognitive faculties.

We can formulate Plantinga’s argument as follows:^[14]

1. The probability that our cognitive faculties are reliable, given naturalism and evolution, is low. 


2. If someone believes in naturalism and evolution and sees that, therefore, the probability of his cognitive faculties’ being reliable is low, then he has a defeater for the belief that his cognitive faculties are reliable. 


3.  If someone has a defeater for the belief that his cognitive faculties are reliable, then he has a defeater for any belief produced by his cognitive faculties (including his belief in naturalism). 


4. Therefore, if someone believes in naturalism and evolution and sees that, therefore, the probability of his cognitive faculties’ being reliable is low, then he has a defeater for the reliability of his belief in naturalism.

EAAN, if sound, does not prove that naturalism is false but that it cannot be rationally affirmed. It is a self-defeating position.^[15]

As Hasker perceptively recognized, EAAN is not so much an argument against naturalism as an argument against materialism.^[16] If the naturalist were to embrace dualism-interactionism, he would be immune to the argument, despite his denial of supernatural realities like God. For though a naturalist, he would recognize the reality and causal efficacy of souls and, hence, their possible selective advantage in the evolutionary struggle for survival. Plantinga himself, in his most recent explication of EAAN, makes it clear that the real target is materialism. Observing that “nearly all naturalists are also materialists with respect to human beings,”^[17] he asks what the likelihood is that the content of our beliefs is in fact true, “given evolution and naturalism (construed as including materialism about human beings).”^[18] He then proceeds to explore the reasons for premiss (1), first, on the assumption of reductive materialism and, second, on the assumption of non-reductive materialism.^[19] Accordingly, “EAAN” is something of a misnomer; the argument is better called the Evolutionary Argument against Materialism (EAAM).

But even that new label is not quite correct. For many naturalists, most eminently W. V. O. Quine, are not materialists but embrace wholeheartedly the reality of immaterial abstract objects such as mathematical entities.^[20] Despite their denial of materialism such thinkers would still be vulnerable to Plantinga’s argument, since they deny that immaterial entities exert any causal influence on the world. As Hasker discerns, what Plantinga’s argument is really about is the so-called causal closure of the physical (CCP).^[21] As defined by philosopher of mind Jaegwon Kim, “This is the assumption that if we trace the causal ancestry of a physical event, we need never go outside the physical domain.”^[22] The closure principle requires that all physical events have only physical causes. If there do exist immaterial entities, they are irrelevant because of the causal closure of the physical domain. Materialists may embrace or deny the reality of mental states of awareness, but they all deny their causal efficacy in the material world. Plantinga’s argument is therefore best cast as the Evolutionary Argument against the Causal Closure of the Physical (EAACCP).^[23]

Plantinga’s argument is thus directly relevant to the present objection based on the impossibility of causal interaction between the soul and body. If EAACCP is sound, then the materialist’s claim cannot be rationally affirmed and collapses in self-defeat. Hasker wryly comments, “To say that this constitutes a serious problem for physicalism seems an understatement.”^[24]

Is EAACCP successful? Andrew Moon, in a careful analysis of global debunking arguments, explains that the crucial question in assessing the success of Plantinga’s argument is, “Which beliefs may the materialist legitimately use to respond to such a potential defeater?” The materialist might think that he can offer a defeater-defeater for Plantinga’s defeater of the reliability of the materialist’s cognitive faculties. He might, for example, invite us to just look around and see how reliable our and other animals’ cognitive faculties are in navigating successfully the physical world. Unfortunately, Moon explains, the materialist, while engaging in such reasoning, would be employing the very cognitive faculties that he already has reason to distrust. In other words, any potential defeater-defeater will itself already be defeated by the original defeater of the reliability of one’s cognitive faculties. Therefore, the materialist cannot block defeat by appeal to a defeater-defeater, since all of his beliefs are already defeated.

Rather what the materialist needs is what Plantinga calls a defeater-deflector.^[25] The materialist might argue that even if the probability R that our cognitive faculties are reliable is low, given our belief in CCP & E, nevertheless there could be other beliefs B that we also hold, such that on CCP & E & B together the reliability of our cognitive faculties R is not improbable. B then serves as a defeater-deflector for the potential defeater, that is, B prevents the admittedly low probability of the reliability of our faculties given CCP & E from being a defeater for the reliability of our faculties.

While a defeater-defeater assumes that some belief is a defeater that must in turn be defeated, a defeater-deflector prevents the belief from being a defeater in the first place. Figuring out exactly which beliefs can legitimately function as defeater-deflectors is a difficult question and constitutes a serious challenge for materialists that needs to be addressed. Plantinga refers to this problem as the conditionalization problem: Which beliefs B are such that if the probability is high that our faculties are reliable given CCP & E & B, then B prevents the defeat of the reliability of our faculties? Clearly, for instance, B cannot just be the belief that our faculties are reliable, for that would be obviously question-begging.

In a recent contribution Moon attempts to solve the conditionalization problem for a certain type of debunking argument that he calls an undercutter-while-rebutter such as he takes Plantinga to offer.^[26] What is needed, says Moon, is a “reliability-promoting, epistemic origin story,” that is to say, an account of how we came to have our cognitive faculties such that, conditional on it, there is a high probability that our cognitive faculties are reliable.^[27] Moon offers what he calls an Epistemic Origin Story Solution (EO-Solution) to the conditionalization problem:

EO-Solution. Even if S’s belief that X and Pr(R|X) is low is a potential undercutter-while-rebutter for R, the belief that B and Pr(R|X&B) is high is a defeater-deflector for that potential undercutter-while-rebutter for R if and only if

(a) S is justified (prior to considering the argument at hand) in believing that B and Pr(R|X&B) is high.

(b) B is part of S’s believed epistemic origin story.

In other words, Moon says, a justifiedly believed, reliability-promoting epistemic origin story will deflect a potential defeater for R. Though Moon’s solution to the conditionalization problem is offered only for the undercutter-while-rebutter interpretation of Plantinga’s argument, there seems to be no reason why it would not apply to what Moon calls the undercutter-because-rebutter interpretation of EAACCP as well. In both cases, the reason that we should conditionalize R on a justifiedly believed, epistemic origin story in order to determine whether R gets defeated is that one must prevent defeat from happening in the first place. Moon writes,

Why is the justifiedly believed epistemic origin story what R should be conditionalized on to determine whether R gets defeated? . . . Given the powerful undercutting power of undercutters-while-rebutters, most bits of evidence one would like to appeal to to deflect the potential defeater will get undercut. To prevent defeat, one must prevent the undercutting from happening in the first place. The appropriate deflector to such a potential defeater will be the set of justifiedly believed propositions in one’s justifiedly believed epistemic origin story, propositions that make probable and explain why R is true. This will prevent undercutting from happening in the first place.^[28]

What is said here of undercutters-while-rebutters could with equal justice be said of undercutters-because-rebutters: to prevent defeat, one must prevent the rebutting from happening in the first place. That requires an epistemic origin story.^[29]

So the question is whether the materialist can offer a justifiedly believed, reliability-promoting epistemic origin story. It is very hard to see how he can. We know that the probability that our faculties are reliable given CCP & E is low. E already includes the materialist’s epistemic origin story. Is there something that could be added to E consistent with materialism that would do the job? It is hard to see what that could be. Given the causal closure of the physical, there seems to be nothing that might be added to E that would raise the probability that our cognitive faculties are reliable.^[30]

It is not clear, therefore, what defeater-deflector the materialist can offer to stave off defeat by Plantinga’s argument. Unless and until such a defeater-deflector can be identified, belief in the causal closure of the physical is irrational. Therefore the objection based on the problem of causal interaction cannot be rationally affirmed.

Conclusion

In sum, the most widespread and influential philosophical objection to substance dualism and, hence, to divine incorporeality fails. Ultimately, physical causation is just as inexplicable as mental causation. Given the sound arguments for a transcendent Creator and Designer of the universe, we can be confident that God can causally interact with the physical world, even if we do not understand how, just as, given our direct acquaintance with ourselves and the arguments for the existence of the soul, the dualist-interactionist can be confident that the soul does causally interact with the body, even if we do not understand how. Finally, the impossibility of causal interaction between soul and body and, hence, between God and the world cannot be rationally affirmed, since to affirm the causal closure of the physical is irrational, pending some justifiedly believed, reliability-promoting, materialist, epistemic origin story.